Seafloor geodetic observations around Japan

The construction of a borderless geodetic observation network between land and sea can be a key for better understanding of the processes of great interplate earthquakes occurring beneath the sea. Several institutions in Japan and the U.S.A. are making effort to develop a seafloor geodetic observation system for this purpose. The first trial of precise seafloor positioning at the Kumano Trough using the seafloor geodetic observation system that we have been developing shows that the system can locate the horizontal position of the seafloor reference point within 5 cm standard deviation. The seafloor reference station network around the Japanese islands was expanded after the initial observation. Eleven seafloor geodetic reference stations have been established on the subsea forearc crust of the Japanese islands arc. The observation, where we visit the seafloor reference stations to make measurements two or three times a year, has just been started.